JP2008300098A - Lithium secondary battery - Google Patents

Abstract

A main object of the present invention is to provide a lithium secondary battery with reduced internal resistance and higher output.
The present invention provides a positive electrode current collector, a positive electrode layer formed on the positive electrode current collector, containing a positive electrode active material, a negative electrode current collector, and the negative electrode current collector. A negative electrode layer containing a negative electrode active material; a separator disposed between the positive electrode layer and the negative electrode layer; and an electrolyte containing a lithium salt filled in the positive electrode layer, the negative electrode layer, and the separator. A lithium secondary battery having a lithium ion conductivity improver filled in the separator, the lithium ion conductivity improver being supported on the mesoporous silica and the mesoporous silica, from the mesoporous silica A lithium secondary battery characterized by comprising a lithium ion conductive group or a lithium ion conductive metal oxide having high acidity. Resolve.
[Selection] Figure 1

Description

  The present invention relates to a lithium secondary battery with reduced internal resistance and higher output.

  With the miniaturization of personal computers, video cameras, mobile phones, etc., in the fields of information-related equipment and communication equipment, lithium secondary batteries have been put into practical use because of their high energy density as the power source used for these equipment. It is becoming popular. On the other hand, in the field of automobiles, the development of electric vehicles has been urgently caused by environmental problems and resource problems, and lithium secondary batteries have been studied as power sources for the electric vehicles. In particular, when a lithium secondary battery is put into practical use as a power source for an electric vehicle, the output of the current lithium secondary battery is low, so that the output of the lithium secondary battery needs to be increased.

  For example, in Patent Document 1, by adding mesoporous silica having nano-sized pores to any part of the positive electrode, the negative electrode, and the separator, the freezing point of the electrolyte contained in the pores decreases, It is disclosed that the characteristics are improved. However, since acid-treated mesoporous silica is used, the acidity of mesoporous silica is small, and the phenomenon that the conductivity of lithium ions is improved by improving the acidity cannot be used. It was difficult to reduce.

  Patent Document 2 discloses a separator characterized in that the surface is charged either negatively or positively in an electrolytic solution. This increases the ionization of the electrolyte solution in the vicinity of the separator and improves the lithium ion conductivity by giving the separator surface a surface potential. Further, as a method for obtaining a separator having a high surface potential, specifically, a method of coating the separator with inorganic oxide fine particles is disclosed. However, even when such inorganic oxide fine particles are added, the lithium ion conductivity cannot be sufficiently improved, and it is difficult to reduce the battery internal resistance.

JP 2005-243342 A JP 11-339754 A JP 2004-14127 A JP-A-11-162441 JP 2002-216537 A

  The present invention has been made in view of the above problems, and a main object of the present invention is to provide a lithium secondary battery with reduced internal resistance and higher output.

  In order to achieve the above object, in the present invention, a positive electrode current collector, a positive electrode layer formed on the positive electrode current collector and containing a positive electrode active material, a negative electrode current collector, and the negative electrode current collector A negative electrode layer formed thereon and containing a negative electrode active material, a separator disposed between the positive electrode layer and the negative electrode layer, and the positive electrode layer, the negative electrode layer, and a lithium salt filled in the separator A lithium secondary battery having the electrolyte, wherein the separator is filled with a lithium ion conductivity improver, and the lithium ion conductivity improver is loaded on the mesoporous silica and the mesoporous silica. And a lithium ion conductive group or a lithium ion conductive metal oxide having a higher acidity than the mesoporous silica. .

  According to the present invention, since the lithium ion conductivity is increased on the surface of the lithium ion conductive group or the lithium ion conductive metal oxide having a high surface acidity, the internal resistance of the lithium secondary battery can be sufficiently reduced. And high output. Moreover, since the contact area with the electrolyte is increased by using mesoporous silica, the internal resistance of the lithium secondary battery can be more effectively reduced and the output can be increased.

In the above invention, the lithium ion-conducting group is preferably a sulfonic acid group (-SO 3 _H). This is because the surface acidity is high and the lithium ion conductivity is excellent.

  In the said invention, it is preferable that the said lithium ion conductive metal oxide is a tungsten oxide. This is because the surface acidity is high and the lithium ion conductivity is excellent.

  In the present invention, there is an effect that it is possible to obtain a lithium secondary battery with reduced internal resistance and higher output.

The lithium secondary battery of the present invention will be described in detail below.
The lithium secondary battery of the present invention is formed on the positive electrode current collector, the positive electrode current collector, the positive electrode layer containing the positive electrode active material, the negative electrode current collector, and the negative electrode current collector. A negative electrode layer containing a negative electrode active material, a separator disposed between the positive electrode layer and the negative electrode layer, an electrolyte containing a lithium salt filled in the positive electrode layer, the negative electrode layer, and the separator; A lithium ion conductivity improving material filled in the separator, the lithium ion conductivity improving material being supported on the mesoporous silica and the mesoporous silica, and the mesoporous silica And a lithium ion conductive group or a lithium ion conductive metal oxide having higher acidity.

  According to the present invention, the lithium ion conductivity can be improved by supporting a lithium ion conductive group or a lithium ion conductive metal oxide having higher acidity than the mesoporous silica on the mesoporous silica. The internal resistance of the lithium secondary battery can be sufficiently reduced to increase the output. In addition, since a highly acidic functional group or metal oxide is supported on mesoporous silica, the contact area with the lithium ions present in the electrolyte can be increased, and the lithium ion conductivity can be improved efficiently. Thus, the internal resistance of the lithium secondary battery can be reduced and the output can be increased.

FIG. 1 is a schematic cross-sectional view showing an example of the lithium secondary battery of the present invention. A lithium secondary battery shown in FIG. 1 includes a positive electrode current collector 1, a positive electrode layer 3 containing a positive electrode active material 2, a negative electrode current collector 4, a negative electrode layer 6 containing a negative electrode active material 5, and a positive electrode A separator 7 disposed between the layer 3 and the negative electrode layer 6; and a positive electrode layer, a negative electrode layer, and an electrolyte (not shown) containing a lithium salt filled in the separator. The lithium ion conductivity improving material 8 is contained.
Hereinafter, the lithium secondary battery of this invention is demonstrated for every structure.

1. First, the lithium ion conductivity improving material used in the present invention will be described. The lithium ion conductivity improver used in the present invention is filled in a separator, supported on mesoporous silica and the mesoporous silica, and has a higher acidity than the mesoporous silica, a lithium ion conductive group or lithium ion conductivity. And a metal oxide.

  The lithium ion conductivity improver effectively improves lithium ion conductivity by supporting a lithium ion conductive group or lithium ion conductive metal oxide having higher acidity than mesoporous silica on mesoporous silica. Can be improved. Furthermore, since functional groups or metal oxides with high acidity are supported on mesoporous silica, the contact area with the lithium ions present in the electrolyte can be increased, and lithium ion conductivity can be improved efficiently. Can do.

FIG. 2 is an explanatory view showing an example of a lithium ion conductivity improving material used in the present invention. The lithium ion conductivity improving material shown in FIG. 2 (a) is mesoporous silica and a sulfonic acid group (SO ₃ H) which is supported on mesoporous silica and is a lithium ion conductive group having higher acidity than mesoporous silica. And. On the other hand, the lithium ion conductivity improving material shown in FIG. 2B is mesoporous silica and tungsten oxide (VI) which is supported on mesoporous silica and is a lithium ion conductive metal oxide having higher acidity than mesoporous silica. ) (Chemical formula: WO ₃ ).

  The present invention utilizes the phenomenon that the conductivity of lithium ions increases on the surface of a highly acidic substance. That is, by adding a lithium ion conductivity improver having mesoporous silica and a lithium ion conductive group or lithium ion conductive metal oxide having higher acidity than mesoporous silica to the lithium ion, It is intended to improve conductivity.

  The reason why the lithium ion conductive group improves the lithium ion conductivity has not been clearly clarified, but the presence of a large number of Bronsted acids having proton donating ability such as sulfonic acid groups, for example, in an aqueous solvent. It is presumed that a phenomenon similar to proton hopping conduction by the Grottus mechanism via water molecules or sulfonic acid groups occurs in the vicinity of the non-aqueous solvent used for the electrolyte and the lithium ion conductive group. On the other hand, the reason why a metal oxide with high (surface) acidity improves lithium ion conductivity has not been clearly elucidated.

In the present invention, the lithium ion conductive group or the lithium ion conductive metal oxide has a higher acidity than mesoporous silica. The difference in acidity is not particularly limited, but is preferably a PZC value, for example, 0.1 or more, particularly 0.5 or more, and particularly 1.0 or more. . In the present invention, the acidity of the lithium ion conductive group, lithium ion conductive metal oxide and mesoporous silica can be determined by determining the isoelectric point (PZC) by measuring the zeta potential, The method of determining by the method described in following literature (1), (2), etc. can be mentioned.
Reference (1): Kodansha, super strong acid / super strong base, p4-7
Reference (2): Industrial books, acid-base catalysts, p159-177
Hereinafter, the lithium ion conductivity improving material used in the present invention will be described for each configuration.

(1) Mesoporous silica First, the mesoporous silica used in the present invention will be described. The mesoporous silica used in the present invention carries a lithium ion conductive group or a lithium ion conductive metal oxide described later.

The diameter of the pores of the mesoporous silica is not particularly limited, but for example, it is preferably in the range of 1 nm to 10 nm, particularly in the range of 1.8 nm to 5 nm.
In addition, the specific surface area of the mesoporous silica is preferably, for example, 700 m ² / g or more. This is because the larger the specific surface area, the larger the contact area with the electrolytic solution and the higher the lithium ion conductivity. Such a specific surface area can be calculated as a BET specific surface area from an adsorption isotherm using a BET isotherm adsorption formula.

  The shape of the mesoporous silica is not particularly limited, and examples thereof include a spherical shape and an elliptical sphere. The average particle diameter of the mesoporous silica is preferably in the range of 0.01 μm to 20 μm, particularly preferably in the range of 0.01 μm to 3 μm. When the average particle size of the mesoporous silica is smaller than the above range, the mesoporous silica particles tend to be too fine and the handling property tends to be extremely lowered. On the other hand, when the average particle size is larger than the above range, the migration distance of the electrolyte ion becomes long. This is because there is a tendency for the performance of the system to decrease.

  In the present invention, as the mesoporous silica, for example, mesoporous silica having a radial type structure described in JP-A-2005-243342 can be used.

(2) Lithium ion conductive group and lithium ion conductive metal oxide The lithium ion conductive group and lithium ion conductive metal oxide used in the present invention are supported on the mesoporous silica.

The lithium ion conductive group is not particularly limited as long as it has higher acidity than the above-described mesoporous silica, and specifically, a sulfonic acid group (—SO ₃ H), a carboxylic acid Examples include a group (—COOH) and a hydroxyl group (—OH), and among them, a sulfonic acid group and a carboxylic acid group, particularly a sulfonic acid group is preferable. This is because the acidity is high and the lithium ion conductivity is excellent.

  The amount of the lithium ion conductive group supported on the mesoporous silica is not particularly limited as long as the lithium ion conductivity can be further improved. For example, when the sulfonic acid group is supported, Specifically, the molar ratio S / M between the sulfur S mole and the metal element M mole constituting the mesoporous silica that is the carrier is 0.001 or more, particularly in the range of 0.005 to 0.3, particularly 0.01. It is preferable to be within the range of ~ 0.1.

  The ion exchange capacity of the lithium ion conductivity improving material having the lithium ion conductive group is not particularly limited.

The lithium ion conductive metal oxide is not particularly limited as long as it has higher acidity than the above-mentioned mesoporous silica, and specific examples include transition metal oxides. Examples of the transition metal oxide include tungsten oxides such as tungsten oxide (IV) (chemical formula: WO ₂ ), tungsten oxide (V) (chemical formula: W ₂ O ₅ ), and tungsten oxide (VI) (chemical formula: WO ₃ ). Zirconium oxide such as zirconium dioxide (chemical formula: ZrO ₂ ); Molybdenum oxide such as molybdenum dioxide (chemical formula: MoO ₂ ) and molybdenum trioxide (chemical formula: MoO ₃ ); Vanadium oxide (V) (chemical formula: V ₂ O ₅ ) Such as vanadium oxide; chromium (II) oxide (chemical formula: CrO), chromium (III) oxide (chemical formula: Cr ₂ O ₃ ), chromium oxide (IV) (chemical formula: CrO ₂ ), chromium oxide (VI) (chemical formula: And chromium oxide such as CrO ₃ ). Among these, in the present invention, the lithium ion conductive metal oxide is preferably tungsten oxide. This is because the surface acidity is high and the lithium ion conductivity is excellent.

  The content of the lithium ion conductive metal oxide in the lithium ion conductivity improver is not particularly limited, but for example, in the range of 0.01% by weight to 30% by weight, especially 0.05% by weight to It is preferable to be within the range of 20% by weight, particularly within the range of 0.1% to 10% by weight.

  The coverage of the lithium ion conductive metal oxide on the surface of the mesoporous silica is not particularly limited. For example, it is in the range of 0.005% to 50%, particularly in the range of 0.025% to 30%. In particular, it is preferably in the range of 0.05% to 20%.

(3) Lithium ion conductivity improving material The lithium ion conductivity improving material used in the present invention has the above-described mesoporous silica and the above-described lithium ion conductive group or lithium ion conductive metal oxide. Moreover, the lithium ion conductivity improving material used in the present invention is usually in a powder form.

  The method for producing the lithium ion conductivity improving material used in the present invention is not particularly limited as long as it is a method capable of obtaining the above-described lithium ion conductivity improving material. For example, when obtaining mesoporous silica carrying sulfate ions (sulfonic acid groups), powdery mesoporous silica is added to a sulfuric acid aqueous solution, stirred to form a slurry, and dried to obtain a powder. Examples thereof include a method of further firing the powder. Moreover, when obtaining mesoporous silica which carries lithium ion conductive metal oxides, such as a tungsten oxide, the method of carrying | supporting using the sol-gel method etc. can be mentioned.

2. Next, the separator used in the present invention will be described. The separator used for this invention is arrange | positioned between a positive electrode layer and a negative electrode layer, has a function which hold | maintains electrolyte, and is filled with the electrolyte mentioned later and the lithium ion conductivity improving material mentioned above.

  In the present invention, the method of filling the separator with the lithium ion conductivity improver is not particularly limited, but for example, a method of forming a separator using a lithium ion conductivity improver and a binder resin, and Examples thereof include a method of fixing a lithium ion conductivity improving material on the porous surface of the separator substrate using a binder.

  In a method of forming a separator using a lithium ion conductivity improving material and a binder resin, the lithium ion conductivity improving material is usually filled by fixing the lithium ion conductivity improving material with a binder resin as a separator. . Thereby, the separator comprised from a lithium ion conductivity improvement material and binder resin is obtained.

The lithium ion conductivity improving material is the same as that described in “1. Lithium ion conductivity improving material”, and thus description thereof is omitted here.
The binder resin is not particularly limited as long as it can immobilize the lithium ion conductivity improver, and specifically, a resin used for forming a separator, and a binder Examples thereof include resins used as materials.

  The resin used for forming the separator can be the same as that used for a general lithium secondary battery, and is not particularly limited. Examples thereof include resins such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide. Especially in this invention, it is preferable that the said resin is olefin resin, such as polyethylene (PE) and a polypropylene (PP). When such a resin is used, the separator can be obtained by, for example, kneading, heating and melting the above-described lithium ion conductivity improving material and binder resin and extrusion-molding.

  In addition, when the resin used to form such a separator is used, the content of the lithium ion conductivity improver contained in the obtained separator is improved by improving the lithium ion conductivity, There is no particular limitation as long as a lithium secondary battery having a sufficiently reduced internal resistance and a high output can be obtained. For example, it is preferably in the range of 30% by mass to 90% by mass, particularly in the range of 40% by mass to 80% by mass, and particularly in the range of 50% by mass to 80% by mass. Within the above range, lithium ion conductivity can be improved, a desired high output lithium secondary battery can be obtained, and the flexibility of the separator such as bending can be maintained. Because. The obtained separator may be any of a non-stretched film, a uniaxially stretched film, and a biaxially stretched film.

  On the other hand, the resin used as the binder is not particularly limited as long as it is used for a general lithium secondary battery. Specifically, polyvinylidene fluoride (PVDF), poly Examples thereof include fluorine resins such as tetrafluoroethylene (PTFE) and ethylenetetrafluoroethylene (ETFE). Among them, in the present invention, polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE) are preferable. When such a resin is used, for example, a solution containing a lithium ion conductivity improver, a binder resin, and a solvent is prepared, and the solution is applied on the negative electrode layer or the positive electrode layer and dried. A separator can be obtained.

  Further, when the resin used as such a binder is used, the weight ratio of the binder to the lithium ion conductivity improver is to improve the lithium ion conductivity, There is no particular limitation as long as a lithium secondary battery having sufficiently high resistance and high output can be obtained. Specifically, the lithium ion conductivity improver is, for example, in the range of 300 parts by weight to 3000 parts by weight, particularly in the range of 500 parts by weight to 2500 parts by weight, particularly 1000 parts by weight with respect to 100 parts by weight of the binder. It is preferable to be within the range of ˜2000 parts by weight. If it is in the said range, the lithium secondary battery which improved the electroconductivity of lithium ion and made desired high output can be obtained.

  Further, in the method of fixing the lithium ion conductivity improving material to the porous surface of the separator substrate using the binder, a solution containing the lithium ion conductivity improving material and the binder is usually applied to the separator substrate. By applying, a lithium ion conductivity improving material is filled. Thereby, the separator which has a separator base material and the lithium ion conductivity improvement material carry | supported on the porous surface of the said separator base material can be obtained. The lithium ion conductivity improving material is the same as that described in “1. Lithium ion conductivity improving material”, and thus description thereof is omitted here. Moreover, about the said binder, the thing similar to the material of the binder mentioned above can be mentioned.

  As said separator base material, the thing similar to the separator base material used for the general lithium secondary battery can be used, It does not specifically limit, It is used in order to form the separator mentioned above. The same resin can be used. Of these, polyethylene and polypropylene are preferred. The separator substrate may have a single layer structure or a multilayer structure. Examples of the separator base material having a multilayer structure include a separator base material having a two-layer structure of PE / PP and a separator base material having a three-layer structure of PP / PE / PP. Furthermore, in the present invention, the separator substrate may be a nonwoven fabric such as a resin nonwoven fabric or a glass fiber nonwoven fabric.

  Examples of a method for applying a paste containing a lithium ion conductivity improver to the separator substrate include a spray method, a dispensing method, a dipping method, a blade coating method, and the like.

3. Next, the positive electrode layer and the negative electrode layer used in the present invention will be described.
The positive electrode layer used in the present invention contains at least a positive electrode active material and an electrolyte described later.
The positive electrode active material is not particularly limited as long as it can occlude and release lithium ions. Examples thereof include LiCoO ₂ , LiCoO ₄ , LiMn ₂ O ₄ , LiNiO ₂ , and LiFePO _4. Among these, LiCoO ₂ is preferable.

  The positive electrode layer usually contains a conductive material and a binder. Examples of the conductive material include carbon black and acetylene black. Since the binder is the same as that described in “2. Separator”, description thereof is omitted here.

On the other hand, the negative electrode layer used in the present invention contains at least a negative electrode active material and an electrolyte described later.
The negative electrode active material is not particularly limited as long as it can occlude and release lithium ions. For example, metal lithium, lithium alloy, metal oxide, metal sulfide, metal nitride, and graphite And carbon-based materials such as Of these, graphite is preferable.

  The negative electrode layer may contain a conductive material and a binder as necessary. As the conductive material and the binder, the same materials as those for the positive electrode layer can be used.

4). Electrolyte Next, the electrolyte used in the present invention will be described.
In the present invention, the separator, the positive electrode layer, and the negative electrode layer described above usually have an electrolyte containing a lithium salt.
Specifically, the electrolyte may be liquid or gelled, but is preferably liquid. Among these, a nonaqueous electrolytic solution is preferable. This is because the lithium ion conductivity becomes better. The non-aqueous electrolyte usually has a lithium salt and a non-aqueous solvent. The lithium salt is not particularly limited as long as it is a lithium salt used in a general lithium secondary battery. For example, LiPF ₆ , LiBF ₄ , LiN (CF ₃ SO ₂ ) ₂ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiC (CF ₃ SO ₂ ) ₃ and LiClO ₄ . On the other hand, the non-aqueous solvent is not particularly limited as long as it can dissolve the lithium salt. For example, propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, 1,2-dimethoxy Ethane, 1,2-diethoxyethane, acetonitrile, propionitrile, tetrahydrofuran, 2-methyltetrahydrofuran, dioxane, 1,3-dioxolane, nitromethane, N, N-dimethylformamide, dimethyl sulfoxide, sulfolane, γ-butyrolactone, etc. Can be mentioned. In the present invention, these non-aqueous solvents may be used alone or in combination of two or more. Moreover, room temperature molten salt can also be used as said non-aqueous electrolyte.

5. Next, the positive electrode current collector and the negative electrode current collector used in the present invention will be described.
In the present invention, as illustrated in FIG. 1, a positive electrode current collector and a negative electrode current collector are usually disposed outside the positive electrode layer and the negative electrode layer, respectively.
Such a positive electrode current collector collects current from the positive electrode layer. The material of the positive electrode current collector is not particularly limited as long as it has conductivity, and examples thereof include aluminum, SUS, nickel, iron and titanium. Among them, aluminum and SUS are preferable. . Furthermore, the positive electrode current collector may be a dense metal current collector or a porous metal current collector.
The negative electrode current collector is a current collector for the negative electrode layer. The material for the negative electrode current collector is not particularly limited as long as it has electrical conductivity, and examples thereof include copper, stainless steel, nickel, and the like, among which copper is preferable. Furthermore, the positive electrode current collector may be a dense metal current collector or a porous metal current collector.

6). Others The lithium secondary battery of the present invention is usually produced by inserting a lithium secondary battery as exemplified in FIG. 1 into a battery case and sealing the periphery thereof. As the battery case, generally, a metal case is used, for example, a stainless steel case. Further, the shape of the battery case used in the present invention is not particularly limited as long as it can accommodate the separator, the positive electrode layer, the negative electrode layer, and the like described above. , Coin type, laminate type and the like.

  The method for producing a lithium secondary battery of the present invention is not particularly limited as long as a desired secondary resistance can be reduced and a high-power lithium secondary battery can be obtained. For example, using a coin cell as a battery case, a negative electrode is placed on a negative electrode can, and the non-aqueous electrolyte is dropped onto the negative electrode. Next, a method of obtaining a lithium secondary battery by placing the separator, dropping the non-aqueous electrolyte, placing a positive electrode, and caulking a positive electrode can can be exemplified.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

  Hereinafter, the present invention will be described in more detail with reference to examples.

[Experiment 1]
Powdered mesoporous silica (SILFAM-A type, manufactured by Nippon Chemical Industry Co., Ltd.) and polytetrafluoroethylene (PTFE) were weighed and mixed at a volume ratio of 50/1 (vol / vol). About 2 cm ^{3 of} this mixture was put into a mold and pelletized. At this time, the pressure was 1 t / cm ² and the pellet shape was a cylinder of φ13 mm. The pellet was dried at 120 ° C. for 12 hours.
Next, an electrolyte solution (ethylene carbonate (EC) and dimethyl carbonate (DMC) mixed sufficiently in a volume ratio of 3: 7) in the pellet pores was mixed with lithium hexafluorophosphate (LiPF ₆ ) as a supporting salt. Was dissolved at a concentration of 1 mol / L), sandwiched between SUS plates, and a conductivity cell filled with an electrolyte solution between the SUS plates was produced.

[Experiment 2]
Conductivity cell in the same manner as in Experimental Example 1, except that sulfate ion (sulfonic acid group) -supported mesoporous silica (described in the adjustment of sulfate ion-supported mesoporous silica in Examples described later) was used instead of mesoporous silica. Was made.

(Lithium ion conductivity measurement)
In Experimental Examples 1 and 2, the thickness and weight of the pellets after drying at 120 ° C. for 12 hours were measured, and the solid content volume ratio was calculated. From this, the volume of the pores in the pellet was derived.
Next, using the conductivity cells obtained in Experimental Example 1 and Experimental Example 2, the lithium ion (Li ⁺ ) conductivity of the pellet was derived by impedance measurement.
Lithium ion conductivity in the pellet pore was derived by calculation using the volume of the pore in the pellet and the lithium ion (Li ⁺ ) conductivity of the pellet. The result is shown in FIG. As shown in FIG. 3, the lithium ion conductivity in the pellet pores is higher in Experimental Example 2 using sulfate ion-supported mesoporous silica (SiO ₂ —SO ₃ H) as a lithium ion conductivity improver. It became larger than the case of Experimental Example 1 using mesoporous silica (SiO ₂ ).

[Example]
(Preparation of sulfate ion-supported mesoporous silica) (see JP 2002-216537 A)
Distilled water was added to 0.5 g of concentrated sulfuric acid (sulfuric acid concentration 96%) to prepare a sulfuric acid aqueous solution having a total weight of 100 g. 20 g of powdered mesoporous silica (SILFAM-A type, manufactured by Nippon Chemical Industry Co., Ltd.) was added to this aqueous sulfuric acid solution and stirred for 3 hours to prepare a slurry. This slurry was heated from room temperature to 100 ° C. at a rate of temperature increase of 5 ° C./min, and water was removed by maintaining at 100 ° C. for 3 hours in an air atmosphere. Then, the white powder was obtained by heating to 200 degreeC with the temperature increase rate of 1 degree-C / min, and hold | maintaining at 200 degreeC for 3 hours by an atmospheric condition. The white powder is further heated to 500 ° C. at a temperature rising rate of 1 ° C./min, and held at 500 ° C. for 3 hours in an air atmosphere. A white powder of sulfate ion-supported mesoporous silica having a molar ratio S / M of 0.03 to a certain hydroxide and / or metal element M constituting the oxide was obtained.

(Separator production)
As a lithium ion conductivity improver, a mixture of 50 parts by weight of white powder obtained by adjusting the above-mentioned sulfate ion-supported mesoporous silica, 15 parts by weight of high density polyethylene having a weight average molecular weight of 1.4 million, and 35 parts by weight of mineral oil was mixed. After smelting and heating and melting, it was formed into a 0.1 mm film by a twin screw extruder. Next, the inorganic film is stretched in the longitudinal direction and the transverse direction by a tenter type stretching machine heated to 140 ° C., and further subjected to heat treatment at 145 ° C. for 15 seconds in an air atmosphere. It was immersed to extract and remove the mineral oil in the film, and dried to prepare a separator having a film thickness of 25 μm, high-density polyethylene 20 wt%, and the above powder 80 wt%.

(Preparation of positive electrode)
In 125 mL of a solvent n-methylpyrrolidone solution in which 5 g of polyvinylidene fluoride (PVDF) as a binder is dissolved, 85 g of lithium cobaltate (LiCoO ₂ ) powder as a positive electrode active material and 10 g of carbon black as a conductive material. It was introduced and kneaded until uniformly mixed to prepare a positive electrode paste. This positive electrode paste was applied on one side onto a 15 μm thick Al current collector, and then dried to produce an electrode. The electrode basis weight was 6 mg / cm ² . This electrode was pressed to a paste thickness of 45 μm and a paste density of 1.6 g / cm ³ . This electrode was cut out to have a diameter of 16 mm to obtain a positive electrode.

(Anode production)
92.5 g of graphite powder as a negative electrode active material is introduced into 125 mL of a solvent n-methylpyrrolidone solution in which 7.5 g of polyvinylidene fluoride (PVDF) as a binder is dissolved, and kneaded until uniformly mixed. Thus, a negative electrode paste was prepared. This negative electrode paste was applied on one side onto a 15 μm thick Cu current collector, and then dried to produce an electrode. The electrode basis weight was 4 mg / cm ² . This electrode was pressed to a paste thickness of 20 μm and a paste density of 1.2 g / cm ³ . This electrode was cut out to a diameter of 19 mm to obtain a negative electrode.

(Coin cell production)
A CR2032-type coin cell was obtained using the obtained separator, positive electrode and negative electrode. In addition, as a supporting salt, lithium hexafluorophosphate (LiPF ₆ ) was dissolved at a concentration of 1 mol / L in a mixed solution in which ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed at a volume ratio of 3: 7. What was done was used.

[Comparative example]
A coin cell was obtained in the same manner as in Example except that mesoporous silica was used instead of sulfate ion-supporting mesoporous silica as the lithium ion conductivity improving material.

[Evaluation]
(Battery resistance measurement)
Li (lithium) ion resistance was measured using the coin cell obtained by the Example and the comparative example. The Li ion resistance was conditioned at 3.0 V to 4.1 V, adjusted to 60% SOC (state of charge), and measured by an AC impedance method at 25 ° C. and a frequency of 10 mHz to 100 kHz. The obtained resistance values are shown in Table 1.

  As shown in Table 1, in the example, the resistance value was 5.0Ω. On the other hand, in the comparative example, the resistance value was 6.0Ω. Thus, the Example using the sulfate ion-supported mesoporous silica as the lithium ion conductivity improving material had a lower Li ion resistance than the comparative example using the mesoporous silica as the lithium ion conductivity improving material.

  From the above results, the coin cell obtained in the example has mesoporous silica and mesoporous silica supported on mesoporous silica in the separator, and having mesoporous silica loaded with sulfate ions having higher acidity than mesoporous silica. As a result, it became clear that the conductivity of lithium ions is higher and the internal resistance can be further reduced. As described above, in the example, it was possible to obtain a lithium secondary battery with high output by reducing the internal resistance.

It is a schematic sectional drawing which shows an example of the lithium secondary battery of this invention. It is explanatory drawing explaining the lithium ion conductivity improvement material used for this invention. It is a graph which shows the lithium ion conductivity measurement result of the conductivity cell obtained in Experimental example 1 and Experimental example 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Positive electrode collector 2 ... Positive electrode active material 3 ... Positive electrode layer 4 ... Negative electrode collector 5 ... Negative electrode active material 6 ... Negative electrode layer 7 ... Separator 8 ... Lithium ion conductivity improving material

Claims (3)

A positive electrode current collector, a positive electrode layer formed on the positive electrode current collector and containing a positive electrode active material, a negative electrode current collector, and a negative electrode layer formed on the negative electrode current collector and containing a negative electrode active material A lithium secondary battery comprising: a separator disposed between the positive electrode layer and the negative electrode layer; and an electrolyte containing a lithium salt filled in the positive electrode layer, the negative electrode layer, and the separator. ,
The separator is filled with a lithium ion conductivity improver, the lithium ion conductivity improver is supported on mesoporous silica and the mesoporous silica, and has higher acidity than the mesoporous silica. A lithium secondary battery comprising a functional group or a lithium ion conductive metal oxide. The lithium secondary battery according to claim 1, wherein the lithium ion conductive group is a sulfonic acid group (—SO ₃ H).   The lithium secondary battery according to claim 1, wherein the lithium ion conductive metal oxide is tungsten oxide.

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